I will look to see what I have in the Curvex, but I can tell you that the Imperial Tank crystals are surprisingly difficult to find. I ended up ordering my last ones from W. S. McCaw, and they are a cylinder style, with slightly raised edges. The originals are flush fit, but sometimes you have to take what you can get.

Thojil
I have several different styles of crystals for the 370-821 but I will need some measurements on the other . I understand you not wanting to remove the old ones yet, so even rough numbers would help me focus.

Thojil
Those helped. I think what you are looking for is a B&B X2495/200 or a Perfit C247/2-199. Neither of which I have. When you remove the crystal , let me know what the actual measurements are and I can look again.

I don't believe you watch is a Curvex Evans. I don't know what it is despite spending some time on it. HolbensFineWatches was nice enough to donate the photos for this post. The illustration is from "The 1950s" page 165. Is is the peaks on the sides of the case that was the tip off for me.

thanks to the forum you now know what you don't have: a Curvex Evans.
If you'd like to know the name of your fine watch: it is a Curvex Marcus.
It can be found on page 245 of Mikes 50s book and was advertised at least three times in May and December 1954.